1. Field of the Invention
The present invention generally relates to an air-fuel ratio control apparatus for controlling the air-fuel ratio of an engine. More specifically, the present invention relates to an air-fuel ratio control apparatus that can reduce cracking of a sensor element of an air-fuel ratio sensor.
2. Background Information
Most vehicles are provided with an exhaust cleaning system that includes an underfloor catalytic converter. When the underfloor catalytic converter is disposed in the exhaust pathway under the floor or in a position set at a distance from the engine for cleaning exhaust that flows from the engine of a vehicle, time is required until activation occurs so as to obtain sufficient cleaning action. On the other hand, positioning the underfloor catalytic converter in the exhaust pathway in a position near the engine poses a problem in that durability is reduced due to thermal degradation.
Some vehicles are provided with an exhaust cleaning system that includes a main (underfloor) catalytic converter and a bypass catalytic converter. One example of this type of exhaust cleaning system is disclosed in Japanese Laid-Open Patent Application No. 5-321644. In this publication, the underfloor catalytic converter is disposed on the downstream side of a main channel of the exhaust channel, and the bypass catalytic converter is disposed in a bypass channel on the upstream side of the underfloor catalytic converter. A switching valve for switching the exhaust flow between the main channel and the bypass channel is disposed in the main channel on the upstream side from the underfloor catalytic converter. The exhaust thereby flows to the bypass channel until the underfloor catalytic converter is activated, and the exhaust is cleaned by the bypass catalytic converter that is activated early, whereby the exhaust cleaning efficiency of a vehicle can be improved.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved air-fuel ratio control apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.